The ecology of giant kelp forests in California - USGS National ...

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occupation of breeding areas in Baja California, Mexico (Rice and Wolman 1971; Oliver et al. 1983). However, there is now evidence that gray whales, while migrating, feed on dense swarms of mysid shrimp within or along the outer edges of kelp beds and forests (Wellington and Anderson 1978, Poole in press, Murison et al. in press). It may be advantageous for a gray whale cow with a dependent calf to supplement her stored reserves by feeding upon the abundant mysid resource associated with kel p (Poole in press). Ki 1 ler whale (Orcinus orca). The status and distribution of the Cal ifornia population of killer whales are not known (Morejohn 1977). Killer whales feed in small groups i n nearshore regions, particularly near areas of high marine mama1 concentrations (e.g., pinniped rookeries; Rice 1968). Pods of killer whales have been sighted traveling along the edge of kelp forests (Daugherty and Schuyler 1979). 4.6.2.4 Pinnipeds. Harbor seal (Phoca vitulus). Harbor seals are yearround residents of embayments, sloughs, and rivers along the California coast, with an estimated population of 20,000 individuals (Miller pers. comm. ). Jones (1981) describes the diet of harbor seals as consisting of shallow-bottom fishes that 1 ive near rock habitat, but they also feed on pelagic fishes in many areas (Estes pers. comm. ). Green1 i ngs and surfperch, two common groups of kelp forest fishes (see Section 4.5), were included by Jones as major prey items. Daugherty and Schuyler (1979) pointed out that harbor seals resting in thick beds of kelp with their heads protruding above the surface are often mistaken for sea otters. Although we could locate no specific reference to the harbor seal's association with kel p beds, individual s are commonly observed while diving in kelp and probably forage extensively in kelp forests when these habitats are close to seal haul-out areas. Jameson (pers. corn.) has even observed a harbor seal partially hauled-out on a dense, floating canopy of Nereocystis luetkeana. California sea 1 ion (Zalophus californianus). The California sea 1 ion breeds on the Channel Islands of southern California, along the coast of Baja California, Mexico, and in the Gulf of California during June and July. During the remainder of the year, some 75,000 sea lions (Bonnell pers. corn.) inhabit the entire coastal region of California. Groups of sea lions are sometimes seen passing through kelp forests or foraging along the kelp forest fringe. Sea lions show a preference for pelagic prey items (Jones 1981). It is probable that the association of sea lions with kelp forests is 1 imited to transitory foraging, a1 though these animal s are commonly observed in kelp forests by divers. 4.6.2.5 Steller'sseacow(Hydrodamalis gigas). Giant kelp forests were, in the oast. orobablv also inhabited bv the now-'extinct ~tellir's sea cow. hi; huge (6,000 kg, over 7 m long; Domning 1978) herbivorous mammal is believed to have inhabited nearshore areas from Baja California, Mexico, to Russia. Probably as a result of hunting by aboriginal man, only an estimated 2,000 animals remained in the remote portions of the western Aleutian Islands and eastern Ru,ssia by 1741, and the last animal is be1 ieved to have been killed in 1768 (Domning 1978). Hydrodamalis gigas apparently did not com~letelv submerse, and fed on various seaweeds -and sea grasses in very shallow (probably 1-2 m) water (Domning 1978). Its shallow subtidal habitat, lack of diving, and slow movements made this sirenian easy prey for hunters. Dayton (1975) suggested that sea cow grazing may have been important in the evolution of algal assemblages in kelp forests. However, given what is known of the sea cow's habitat and method of feeding, this is arguable. A1 though apparently never observed, sea cows could have fed on surface canopies in deeper water. 4.7 DISEASES 4.7.1 Introduction A variety of pathogens and parasites infect macro-organisms in giant kelp forests, but except for a limited number of cases reviewed below, little is known of their effects on host populations.
4.7.2 Macroalgae Andrews (1977) and Goff and Glasgow (1980) recently summarized information on pathogens, and the latter publication is a particularly comprehensive account. Perhaps the most notorious disease is "black rot" of Macrocystis, which is visible as dark areas on the margins of the blades. These become lesions, and the blades eventually disintegrate. The symptoms may occur throughout large kelp stands, suggesting that the disease may cause large-scale loss of plants (ZoBell 1946). Scotten (1971), however, could not find evidence of a bacterial or fungal cause, and suggested that black rot is not caused by a pathogen, but may simply be deterioration associated with elevated water temperatures. Dean (pers. comm.) observed extensive black rot and numerous sinking fronds in southern California kelp forests in October 1983, coincident with the warm water associated with the current "El Nino" (see Section 2.3). Recent observations of adult Macrocystis pyrifera isolated in a large container at Santa Catal ina Is1 and 1 revealed another potential disease (Gerard pers. comm. ). Blades (especi a1 ly those near the holdfast) growing in warm, high nutrient water developed numerous small holes and eventually deteriorated. Dean (pers. comm.) noted similar svmotoms in small pterYgbphora cal ifornica 'off San Onofre in 1983. The svmotoms in Macrocystis led to the tentatiiv'e name of "shot hole disease," but the cause is unknown. However, just as in monocultures of terrestrial plants, the common occurrence in culture of this hitherto rarely observed symptom suggests that other unanticipated problems with disease may occur in future attem ts to isolate Macrocystis in culture [see Goff and Glasgow 1980 for a review of pathogens in other currently-cul tivated seaweeds). Macrocystis as well as other macroalgae are inhabited by a diverse group of potential pathogenic organisms such as nematodes, algal and animal epigrowths, algal parasites , bacteria, and fungi. Plants may be found with tumors and gal 1s (Andrews 1977, Goff and Glasgow 1980). Few of these have been observed to cause severe damage tc, fndividuals in kelp forests, and none has been observed to cause damage to populations. 4.7.3 Invertebrates Invertebrate pathogens and parasites are also common, and some have significant impacts on populations. Pearse et al. (1977) reported a mass mortalitv of red sea urchins (~tron~~lkentrotus franciscanus) near Santa Cruz, and reviewed other occurrences of this phenomenon in California. When affected, the urchins' spines are no longer held upright and are eventually lost, the epidermis degenerates, and the animal dies. Similar symptoms and widespread mortal i ty have occurred recently in sea urchin populations in Nova Scotia (Miller and Colodey 1983). The cause of the disease in California is unknown; a protozoan may be the cause in Nova Scotia (Miller and Colodey 1983). If sea urchin grazing 1 imits kelp distribution, then such a disease can ultimately result in kelp forest enlargement, as it did at the site near Santa Cruz (Pearse and Hines 1979), and as it is doing in Nova Scotia (Pearse pers. comm. ). Observations in these and other areas suggest that disease may be an important factor in the regulation of sea urchin populations (Pearse pers. comm. ) , Mortali tv of other echinoderms. particularly " the bat star (patiria miniata) has been observed in southern Ca1 ifornia, both along the mainland (Schroeter and Dixon pers. comm.) and at San Nicolas (Harrold pers. comm.) and Santa Catal ina Island (Gerard pers. comm.). Similar mortality has occurred in the Gulf of California (Dungan et al. 1982). When the water is abnormally warm, bat stars become covered with a white, mold-1 ike film and eventually die. Affected bat stars that fell down steep slopes into colder water at Santa Catalina Is1 and a~~arentl v recovered. Schroeter et al. (1983) have shown that P. miniata predation may significantly a1 ter the distribution and abundance of white sea urchins (Lytechinus anamesus), and feeding by the star may also significantly affect other populations, including plants (see Section 4.4.3 above). Bat star populations have been nearly destroyed by
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This is one of the first reports to
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DISCLAIMER The mention of trade nam
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on North's publications for informa
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Paye 3.6 Biomass. Productivity. and
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.................... 5.5 Effects of
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FIGURES Number 1 The morphology and
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TABLES Page 1 Factors influencing k
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CONVERSION TABLE Metric to U.S. Cus
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CHAPTER 1 INTRODUCTION I know few t
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A. Holdfast morphology of Macrocyst
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Figure 2. The geographic distributi
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Lorria. A succession of proy rams d
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CHAPTER 2 THE ABiOTiC ENVIRONMENT E
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floating masses as Sargdssunl does
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(deeper) margin of the Point Lorna
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2.5. NuTRI ENTS Table 3. Known nutr
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and Lindley 1980) indicated that se
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shell debris during periods of surq
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than % 5 m, and deeper than about Z
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3.2.2 Other Kelp Forests Pacific is
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spe~ieb i i ~ a i Lar~ vc~ut ;IT cn
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--P auunaance OT red bed ur L ~ I ~
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Coral 1 i na chi lensis, Li thothri
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considerable spatial var~ation with
Page 51 and 52: organ1 sms tnemsei ves , parxi cui
Page 53 and 54: enhancement of colonization by mi c
Page 55 and 56: (1973), we could find no published
Page 57 and 58: Table 5. ~acrocystis pyrifera net p
Page 59 and 60: GENERALIZED FOOD WEB FOR A MACROCYS
Page 61 and 62: GENERALIZED CONTROL WkB FOR MACROCY
Page 63 and 64: that migrate between the benthos an
Page 65 and 66: features of the environment. [see L
Page 67 and 68: It remains unclear whether sites wh
Page 69 and 70: obs.) now suggest that growth rings
Page 71 and 72: m depth (Velimirov et a1. 1977, Die
Page 73 and 74: I o NEEDLE ROCK o POINT SANTA CRUZ
Page 75 and 76: there is such overlap, we have put
Page 77 and 78: Bryozoans are commonly among the fi
Page 79 and 80: forests, and many feed on detritus
Page 81 and 82: Table 6. Common invertebrate grazer
Page 83 and 84: 7 I~I- Table 7. Concentration and b
Page 85 and 86: uncinata build tubes in kelp laiiri
Page 87 and 88: 4.4.4.2 Moll uscs (Moll usca). Seve
Page 89 and 90: ..,........................ Blue Ro
Page 91 and 92: Predators feeding on 1 arge, mobile
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Page 96 and 97: Table I@. Birds of kelp forests and
Page 98 and 99: described Brandt ' s cormorants in
Page 100 and 101: winter storms. The forests may also
Page 104: disease in one kelp stanO'r, southe
Page 107 and 108: Plate 2A. The 1 ined chiton Tonicel
Page 109 and 110: The Gauntiet of Macrocystis Micr~sc
Page 111 and 112: (1) the "northern lethal boundary"
Page 113 and 114: have different physiological tolera
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Page 117 and 118: elating to the effects of one lamin
Page 119 and 120: There is some information on densit
Page 121 and 122: 5.6.1 Invertebrate Grazers (Other T
Page 123 and 124: differences a1 ong coast1 i nes occ
Page 125 and 126: As with previously discussed aspect
Page 127 and 128: CHAPTER 6 HUMAN USE, MANAGEMENT, AN
Page 129 and 130: egrowth from unharvested subsurface
Page 131 and 132: Table 12. Gal i fornia, ~0miller~id
Page 133 and 134: ,,,tl areas as natural baselines fo
Page 135 and 136: o r i d . 6~i1cr pltfGi~~eCi t.TFt.
Page 137 and 138: L.. - - 4 wnLci , art" CIL s I , it
Page 139 and 140: oil spill occurred. If sea otter po
Page 141 and 142: condition of particular forests wil
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Page 145 and 146: Anonymous. 1958. The marine fish ca
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Page 149 and 150: Day, R.W. , and R.W. Osman. 1981. P
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Foster, M.S., C. Agegian. R. Cowen,
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Hasegawa, Y., and Y. Sanbonsuga. 19
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Kain, J.M. 1982. The reproductive p
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the Atlantic coast of Canada. I. Yc
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Neushul, M., and F.T. Haxo. 1963. S
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ecology and behavior. York. Plenum
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Handbook of phycol ogical methods:
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Tegner, M. J. , and L. A. Levin. 19
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Thistle, eds. Ecological communitie
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North, W. J. California Institute o
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